"The Quite Zone of an anechoic chamber is a defined volume within the chamber where a Device Under Test (DUT) is to be placed for evaluation. Quiet Zone Probing is accomplished by moving a probe antenna through the Quiet Zone to determine the level of extraneous signals entering the volume." (from Sirles, C.W., et al., "Anechoic Chamber Performance Characterization Using Spherical Near-Field Imaging Techniques")

In other words, a quite zone is a specific volume inside the anechoic chamber, wherein the level of RF power does not exceed a certain limit. The "quiteness" of the zone is a function of signal frequency, i.e. different frequencies will correspond to different RF levels within the quite zone volume.

anechoic lesion

anechoic cyst in right overy

Hepatic veins do not have echogenic walls. Anechoic means not having or not producing echoes. The hepatic vein carries blood from the liver.

The purpose of an anechoic chamber is to enable measurements to be made in the absence of reflections or background noise. They may be designed for audio, or radio frequency use.

Commonly wedges of (sound) absorber are mounted on all walls, such that as the (sound) wave approaches the wall, the amount of (sound) absorber is greater.

The folk who work in them walk on a wire grid suspended half way up, though this may be removed for sensitive measurements.

They are commonly mounted on an isolating system, so they are very quiet inside as well. Sometimes a room within a room system.